Handling Back Button in Android without implementing InputProcessor

Please advice/clarifyon below issue in libgdx while handling back button in Screens.

I have already gone through these 2 threads,

http://stackoverflow.com/questions/7223723/in-libgdx-how-do-i-get-input-from-the-back-button

Is there a way to capture back button twice in same activity libgdx game

As per suggestion in above two threads, I have done something like this in 2 Screen of my Game,

public class MainMenuScreen implements Screen{
    //omitted unnecessary code
    @Override
    public void render(float delta) {
    if (Gdx.input.justTouched()) {
        game.setScreen(game.STS);   //Setting 2nd Screen
    } else if (Gdx.input.isKeyPressed(Keys.BACK)) {
        System.out.println("mms back");
        //if(Gdx.input.isKeyJustPressed(Keys.BACK))
        Gdx.app.exit();            // Exiting   
    }
}

public class StageScreen implements Screen{
    //omitted unnecessary code
    @Override
    public void render(float delta) {
        if (Gdx.input.isKeyPressed(Keys.BACK)) {
        System.out.println("backed to mms in android");
        //if(Gdx.input.isKeyJustPressed(Keys.BACK))
        game.setScreen(game.MMS);  //going back to Main screen
    }
}

Above code works fine, when I press BACK in Stage Screen to call Main Screen, it exits the app immediately, without stopping in my Main screen, which is as per my expectations because I am using Gdx.input.isKeyPressed(Keys.BACK) instead of Gdx.input.isKeyJustPressed(Keys.BACK).

But my problem is, when I use Gdx.input.isKeyJustPressed(Keys.BACK) method in my Screens, it does not (return true) catch BACK key.

I have already set Gdx.input.setCatchBackKey(true) for my Game.

Any idea, why does isKeyJustPressed not responds while isKeyPressed does?

Thanks in Advance.